The present invention is directed to transparent substrates having multi-layer coatings for thermal insulation properties, as well as to methods of manufacturing such multi-layer coated articles. The invention relates, in particular, to coated, transparent glass substrates which are heat treatable. Certain preferred embodiments are suitable especially for automotive and architectural applications, exhibiting high visible light transmittance and high infra-red (IR) energy reflectance.
Coated glazing products having anti-solar properties, that is, low transmittance of wavelengths in the infra-red range, are known to those skilled in the art. Coatings for glazing products are disclosed, for example, in European patent application 0 646 551 A1 entitled Heat-Treatment Convertible Coated Glass and Method of Converting Same. That document discloses silver coatings comprising a layer of Si3N4 over a layer of nickel or nichrome, over a layer of silver, over a second layer of nickel or nichrome, over a second layer of Si3N4. Sputtering is disclosed for producing such coating. Sputtered deposition of a multi-layer coating is described, for example, in European Patent Application 0,418,435 to Nalepka. The multi-layer coating of Hayward et al. is said to comprise a layer of sputtered zinc, tin, titanium, indium/tin or bismuth oxide, next a layer of sputtered silver or silver alloy, then a layer sputtered titanium or stainless steel and finally a layer of zinc, tin, titanium, indium/tin or bismuth oxide. Such multi-layer film is said to have excellent visible light transmission while controlling both near infra-red solar energy and far infra-red reflected energy. A temperable coated article is suggested in U.S. Pat. No. 5,552,180 to Finley et al. The coated article of Finley et al. employs a metal-containing film such as titanium nitride which ordinarily oxidizes at the high temperatures encountered during glass tempering, along with an overcoating of a protective layer of a silicon compound and an undercoating with a stabilizing metal-containing layer. In U.S. Pat. No. 3,990,784 to Gelber a multi-layer coating for architectural glass is suggested, comprising first and second metal layers with a dielectric layer disposed between them. Gelber suggests that the transmission properties of the coating can be changed independent of its reflection properties, by varying the thickness of the metal layers while maintaining the ratio of their thicknesses constant.
Similar coatings are disclosed in European Patent Application 97104710.5 published as EP0796 825 A2, wherein a low emissivity sputtered coating employs controlled index of refraction of an undercoat layer of an appropriate dielectric material below a first Si3N4 layer. Also a layer of silver is used, sandwiched between layers of nichrome. The term xe2x80x9cnichromexe2x80x9d is used to designate a layer which includes some combination of nickel and chromium, at least some of which is in its metallic state, although same may be oxidized. In a similar way, the term xe2x80x9csilverxe2x80x9d means that the layer consists essentially of metallic silver, but may include some other elements in small concentrations that do not adversely affect the performance characteristics of the silver in the system as a whole. Bent or toughened silver coated glass is taught in European Patent Application 87300601.9 published as No. 0233 003. An additional layer of aluminum, titanium, zinc, tantalum or zirconium is used over the silver layer, or both over and under the silver layer. In recent years, the popularity of coated glasses has occasioned numerous attempts to achieve a coated glass article which, prior to heat-treatment, can be coated, and which thereafter, can be heat-treated without adversely changing the characteristics of the coating or the glass itself (i.e., the resulting glass article). One of the reasons for this is, for example, that it can be extremely difficult to achieve a uniform coating on an already bent piece of glass. It is well-known that if a flat glass surface can be coated and thereafter bent, much simpler techniques can be used to get a uniform coating than if the glass has been previously bent. This is true for architectural, automotive, and residential glasses.
Various difficulties have been encountered by those skilled in the art in developing commercially suitable coatings for architectural and automotive glazing. In particular, it has proved difficult to achieve coatings which provide good attenuation of direct solar radiation, that is, good anti-solar properties. There has long been need in the glazing industry for coating systems which can be uniformly deposited, especially by sputtering onto large surface areas with fast deposition rates, low deposition power density, good film quality, including high film durability, bulk or near bulk density, and long shelf life. As used here, large area deposition refers to deposition onto transparent substrates suitable in size for architectural and automotive glazing applications.
It is an object of the present invention to provide coated articles meeting some or all of these industry needs. In particular, it is an object of at least certain preferred embodiments of the invention to provide heat-treatable coated glass articles comprising a substantially transparent glass substrate with a substantially transparent coating on the surface of the substrate, which coating has good transmittance of visible light as well as good anti-solar performance characteristics. In accordance with certain preferred embodiments, it is a further object to provide glazing units incorporating such coated glass. It is an object of at least certain preferred embodiments of the invention to provide heat-treatable coated glass articles comprising a substantially transparent glass substrate with a substantially transparent coating on the surface of the substrate, which coating has medium level of transmittance of visible light as well as extremely high anti-solar performance characteristics. Such coated articles can be used for architectural purposes and automotive applications, e.g., windshields with heat shielding properties, or windshields with defrosting and anti-fogging properties.
It is a further object of the invention to provide methods of manufacturing the aforesaid coated articles. In accordance with preferred embodiments, such manufacturing includes applying a coating in accordance with the invention. Optionally, the methods disclosed here further include the steps of applying an electrically conductive bus bar, if desired, and performing heat treatment of the coated article, e.g., bending or tempering, and also optionally conducting laminating processes.
Additional objects and advantages of the present invention will be readily understood by those skilled in the art given the benefit of the following disclosure of the invention and detailed description of preferred embodiments.
In accordance with a first aspect of the invention, a heat-treatable, coated glass article of manufacture comprises a substantially transparent substrate with a substantially transparent multi-layer coating on a surface of the glass substrate. The substantially transparent coating comprises a first anti-reflection layer of dielectric material overlying the surface of the substrate. Preferably, the anti-reflection layer is directly on the surface of the substrate. As used here and in the appended claims, any particular layer of the substantially transparent, multi-layer coating is said to be xe2x80x9cdirectlyxe2x80x9d on or to xe2x80x9cdirectlyxe2x80x9d overlie the substrate or another layer of the coating if no other layer of the coating is positioned between them. In this regard, any particular layer of the coating may be said to lie directly on another layer of the coating notwithstanding that there may be a slight transition zone between the two layers involving migration of the material of one layer into the other and/or interlayer reaction products different from the primary composition of the layers. A first buffer layer, most preferably a chromium buffer layer, overlies the first anti-reflection layer. Preferably it lies directly on the anti-reflection layer. A chromium buffer layer, as that term is used here, means a layer which is essentially metallic chromium, such as a layer deposited by sputtering from a chromium metal target in an inert atmosphere. It may be in part oxidized, especially in preferred embodiments wherein the chromium buffer layer scavanges oxygen from an adjacent silver or copper metal or silver-copper mixed metal IR reflective layer and/or from anti-reflection layers during a heat treatment step, as further discussed below. An infrared reflective layer of silver metal or copper metal or silver-copper mixed metal directly overlies the first chromium buffer layer. A second chromium buffer layer directly overlies the infrared reflective layer. Finally, a second anti-reflection layer of dielectric material overlies the second buffer layer. Preferably, it directly overlies the second buffer layer. Preferably, the first and second anti-reflection layers of dielectric material are SnO2, in view of the good D.C. magnetron sputter deposition properties of SnO2 and its compatibility with other preferred materials of the film stack coating disclosed here. Other suitable anti-reflective materials for use in the coating include other oxide and nitrade materials, such as, for example, WO3, TiO2, ZnO, BiOx and Si3N4. Additional suitable anti-reflection layer materials will be apparent to those skilled in the art given the benefit of this disclosure. Similarly, the use of copper, copper-silver, or most preferably silver in the IR reflective layer, especially with the chromium buffer layers sandwiching it, provides highly durable coatings which are heat-treatable and, in fact, even yield improved spectral properties upon undergoing heat-treatment. That is, especially in preferred embodiments, heat treatment of the system with or without the IR reflective layers shows several significant effects. First, optical transmittance of the coated article improves upon heat treatment. There is a temperature threshold to start transparency improvement, around 400xc2x0 C., to start the oxidation of the buffer layers. Second, electrical resistance reduces upon heat treatment e.g., sheet resistance of 6 Ohm may be reduced to 3 Ohm after heat treatment. This improvement in sheet resistance is believed due to the diminishing of interface scattering at the abrupt Agxe2x80x94Cr. The degree of interface by forming an extended interface of Agxe2x80x94CrOx upon heat treatment. Crystalinity degree of the Ag film may also improve upon heat treatment, producing increased conductivity. This effect is achieved at least in preferred embodiments without noticeable degradation in the IR properties of the system. This excellent electrical conductance of the system allows the electrical heating of the coated glass in certain preferred embodiments by conducting an electrical current through the Ag layer. Third, optical transmittance of the system with anti-reflecting oxide layers improves, as does durability as compared with buffer-silver-buffer three-layer system.
Unless the individual instance of usage clearly indicates otherwise, reference herein to heat-treatable glass should be understood to mean glass with a coating according to the present invention, which has not been heat-treated (but which can undergo heat treatment successfully in accordance with the principles disclosed here) or which has not been heat-treated. The term heat-treated is used to mean glass which has been subjected to a heat-treating process, such as tempering, annealing and/or bending, etc.
It is one advantage of the present invention that the heat-treatable, coated glass articles disclosed here exhibit certain improvements or changes in spectral properties upon undergoing heat-treating (e.g., at temperatures of about 600xc2x0 C.). Visible light transmittance increases and sheet resistance decreases, and both mechanical stability and environmental stability improve with heat-treating. In a typical embodiment employing a multi-layer coating deposited by D.C. magnetron sputtering on clear soda-lime-silica glass having a glass thickness from 2.2 mm thick for an automotive windshield application to 6 mm thick for common architectural applications, using SnO2 layers about 20 nm to 60 nm thick for the anti-reflection layers, chromium buffer layers about 1 to 4 nm thick, and a silver metal IR reflectance layer 6 nm to 17 nm thick, emissivity may improve, typically, from a value of 0.15 to 0.01, visible transmittance may increase or may reduce, e.g., from a value of about 85% to about 70%, and sheet resistance will improve from about 13 Ohm/sq. to only about 1.5 Ohm/sq., with no haze occurring. Thus, the coated glass disclosed here can be used as different products. Before heat treatment, coated glass in accordance with an embodiment of the invention may have grey-blue color and Tvis of 50% to 70%. After heat-treating, the same glass may have Tvis of about 70% to 85% and be colorless.
In accordance with certain preferred embodiments, such heat-treatable, coated glass is especially well-suited for use in motor vehicle windshield applications with high transmittance, low visible light reflectance and high energy reflectance, wherein a polyvinyl butyryl or other suitable polymer sheet is sandwiched between one coated glass sheet as disclosed here and an uncoated sheet. Certain especially preferred embodiments employing a coating having the above five layer coating structure, wherein the first buffer layer is a chromium buffer layer of 2 nm and the second buffer is a chromium buffer layer of 2.5 nm, and the infrared reflective layer is a silver metal layer 10 nm thick, when the glass of the windshield (in total for both glass sheets) is about 2.2 mm thick soda-lime-silica glass, have visible light transmittance greater than 76%, solar energy transmittance less than 50%, and solar reflectance (IR region) of at least 25%. In such especially preferred windshield embodiments, and in other preferred embodiments of the invention disclosed here, the infrared reflector layer is silver and each of the chromium buffer layers has a thickness which is about 10% to 30% of the thickness of the silver layer after heat treatment. In such especially preferred windshield embodiments, and in other preferred embodiments of the invention disclosed here, the first buffer layer is about 20% thinner than the second buffer layer.
In accordance with certain preferred embodiments, such heat-treatable ,bendable, coated glass is especially well-suited for use in architectural applications, especially for round buildings or buildings with cylindrical outside elevators. Certain especially preferred embodiments employing a coating having the above five layer coating structure, wherein the buffer layers are chromium buffer layers of 4 nm for first buffer and 4 nm for the second buffer the infrared reflective layer is silver metal 14 nm thick, and the glass of about 6 mm thick soda-lime-silica glass, have the ratio of visible light transmittance/total solar energy transmittance of about 50/27. This assumes, for example, a 6 mm- 12 mm-6 mm two pane configuration, with the coating at the surface No. 2. Such terminology, when used herein, means that a first 6 mm pane in spaced 12 mm from the second 6 mm No. 1; its inside surface is surface No. 2; etc.
In accordance with another aspect, a heat-treatable coated glass article is provided, having a substantially transparent coating, preferably deposited on soda-lime-silica glass by D.C. magnetron sputtering, wherein the coating comprises:
a first anti-reflection layer of dielectric material overlying the glass substrate
a first buffer layer overlying the first anti-reflection layer
a first infra-red reflective layer of silver metal directly overlying the first buffer layer
a second buffer layer directly overlying the infra-red reflective layer
a second anti-reflection layer of dielectric material overlying the second buffer layer
a third buffer layer overlying the second anti-reflection layer
a second infra-red reflective layer of silver metal directly overlying the third buffer layer
a fourth buffer layer directly overlying the second infra-red reflective layer
a top anti-reflection layer of dielectric material overlying the fourth buffer layer.
In accordance with certain preferred embodiments, such heat-treatable, coated glass is especially well-suited for use in motor vehicle windshield applications, wherein a polyvinyl butyral (PVB) or other suitable polymer sheet is sandwiched between one coated glass sheet as disclosed here and an uncoated sheet. Such preferred embodiments have very low reflectance of visible light and high transmittance of visible light, as well as low total solar energy transmittance and high solar reflectance (IR region). Certain especially preferred embodiments employing a coating having the above nine layer film stack, wherein the buffer layers are chromium buffer layers of 1 nm to 4 nm thickness, the infrared reflective layer is silver metal around 50 nm to 60 nm thick, when the glass of the windshield (in total for both glass sheets laminated with PVB) is about 5.5 mm thick soda-lime-silica glass, have visible light transmittance greater than 75%; total solar energy transmittance less than 50%; and solar reflectance (IR region) of at least 25%. In such especially preferred windshield embodiments, and in other preferred embodiments of the invention disclosed here, each infrared reflector layer is silver and each of the chromium buffer layers has a thickness which is about 10% to 30%, the thickness of the silver layer after heat treatment.
The chromium buffer layers are found to perform a crucial role in rendering the coated glass articles disclosed here durable and effective. Without wishing to be bound by theory, it is currently understood that the chromium buffer layers, although deposited as chromium metal, oxidize to some degree, especially during heat-treatment of the coated glass. The buffer layers oxidize by taking oxygen from adjacent layers, such as SnO2 or other oxide material of an adjacent anti-reflection layer. There is a resulting increase in volume of the chromium buffer layer and corresponding increase in buffer layer density without cracking of the buffer layer. This is highly advantageous, since the buffer layer should be crack-free and void-free following heat treatment to prevent oxygen diffusion through the buffer layer to the silver metal IR reflection layer. Also, the high-density of the buffer layers reduces or eliminates the adverse affects of migration of silver into the buffer layers. Thus, long term durability and performance are achieved in the multi-layer coated, heat-treatable glass articles disclosed here. In preferred motor vehicle windshield embodiments of the present invention, the multi-layer heat-treatable coating is provided on one of the two glass panes which sandwiched between them a PVB sheet. Preferably, the coating is provided on the inside glass pane (i.e., the one facing the exterior pane vehicle passenger compartment rather than the exterior pane), most preferably on the so-called surface No. 2 of the windshield, i.e., on the outside surface of the inside pane (i.e., adjacent the PVB sheet). The two glass panes, one coated and one uncoated, typically are paired and bent together. In accordance with preferred embodiments, special powder to prevent the glass panes sticking together are usually used between the matched panes during such bending process can be eliminated. The multi-layer coating serves to prevent sticking. Moreover, the multi-layer coating in accordance with preferred embodiments is sufficiently durable and though, that it can be placed into contact with the second glass pane during the bending process without causing unacceptable scratching or other degradation of the coating.
In accordance with another aspect of the invention, methods are provided for making the coated article disclosed above. Such methods comprise providing a substantially transparent substrate, typically with appropriate surface preparation steps being performed on the surface to be coated. The multi-layer, anti-solar coating is then formed on the surface of the substrate. The first anti-reflection layer of dielectric material is deposited, followed by the first chromium buffer layer, followed by the silver metal infra-red reflective layer, followed by the second chromium buffer layer, followed by the second anti-reflection layer. In accordance with preferred embodiments, each of the layers of the substantially transparent coating is deposited by sputtering in a series of sputter stations arranged sequentially in a single sputtering chamber through which the transparent substrate passes at constant travel speed. Suitable partitions, such as curtains or the like, separate one sputter station from the next within the sputtering chamber, such that different deposition atmospheres can be employed at different stations. A reactive atmosphere comprising nitrogen or oxygen or both can be used, for example, at a first station to deposit an anti-reflection layer, followed by a non-reactive atmosphere consisting essentially of argon or other suitable inert gas at a subsequent station for depositing the silver metal IR reflection layer.
In accordance with certain highly preferred embodiments of the manufacturing method disclosed here, the substantially transparent coating is deposited by multiple passes, preferably two passes through such multi-station sputtering chamber. If the multi-station sputtering chamber has a sufficient number of cathodes, e.g., at least nine cathode materials mentioned above, this method is especially suitable, for example, for depositing the nine layer coating disclosed above in a single pass. Alternatively, during each of the passes through the sputtering chamber, a multi-layer coating is deposited comprising the aforesaid first anti-reflection layer, first chromium buffer layer, silver metal layer, second buffer layer and second anti-reflection layer. Coatings formed in accordance with such multi-pass methods of the invention are found to have substantially improved coating properties, including especially colour spectral uniformity.
It will be apparent to those skilled in the art in view of the present disclosure, that the present invention is a significant technological advance. Preferred embodiments of the substantially transparent coatings disclosed here have excellent spectral performance characteristics, including excellent transmittance of visible light and advantageously high anti-solar properties, that is, high attenuation levels of direct solar radiation. Employing the above disclosed silver metal infra-red reflective layer, sandwiched between chromium buffer layers, together with the anti-reflection layers results in novel multi-layer coatings which are highly suitable for large area deposition by planar DC magnetron sputtering. Fast deposition rates can be obtained, even employing advantageously low deposition power densities. The resulting coating has high durability, bulk or near bulk density and long shelf life.
Additional features and advantages of the various embodiments of the present invention will be further understood in view of the following detailed description of certain preferred embodiments.